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US4618742A - Method and apparatus for decoding audiofrequency information sent through rotary dialing - Google Patents

Method and apparatus for decoding audiofrequency information sent through rotary dialing Download PDF

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Publication number
US4618742A
US4618742A US06/479,026 US47902683A US4618742A US 4618742 A US4618742 A US 4618742A US 47902683 A US47902683 A US 47902683A US 4618742 A US4618742 A US 4618742A
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output
phone
input
square wave
time period
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US06/479,026
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Horacio Castro
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M11/00—Telephonic communication systems specially adapted for combination with other electrical systems
    • H04M11/06—Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors
    • H04M11/066—Telephone sets adapted for data transmision
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M1/00—Substation equipment, e.g. for use by subscribers
    • H04M1/26—Devices for calling a subscriber

Definitions

  • the field of the invention corresponds to the phone communications art and it is particularly based on the utilization of the transmission of audiofrequency information through rotary dialing from a calling phone set after closure of the d.c. current or conversation circuit established with the called party.
  • the present disclosure applies the universally known SCHMITT-TRIGGER, in this case used as a level comparator.
  • said method comprises the steps of: sending from the calling end of a phone line the series of characters corresponding to the phone number of the called party; after closure of the d.c. current circuit of the called party's phone line, sending audiofrequency signals through rotary dialing from the calling party's end; decoding said audiofrequency signals with the apparatus at the called party; transforming said decoded audiofrequency signals into logic data or into single pulses; and, finally, applying said logic data or single pulses to commanding, ordering or informing means.
  • the proposed apparatus has an input signal limiter to protect its circuits, using for such purposes an adjustable trimmer to establish the proper threshold.
  • the limiter's output is connected to an operational amplifier and to filters suitable for recovering the significant or useful portion of the audiofrequency signals to be analyzed, eliminating the noise components and non-desired signals which may appear in the phone line.
  • Signals thus produced by the operational amplifier and suitably filtered are introduced into a rectifier circuit, which emits a rectified output of said signals to be analyzed, thus eliminating one of the semi-cycles or half-waves of said signals.
  • the output of said rectifier is introduced into a SCHMITT-TRIGGER which converts said signals into square wave signals, establishing their amplitude at certain levels, this requirement due to the wide dynamic range offered by said audiofrequency signals.
  • the output of the SCHMITT-TRIGGER is introduced into a microprocessor that works as an interval comparator and time analyzer. This microprocessor determines, through an accurate measurement of times, the equivalence between the audiofrequency signals generated by a rotary phone and the succession of pulses that make up a pulse train per each dialed character or number.
  • the microprocessor is capable of determining when a train of phone pulses has been completed and ignoring audiofrequency signals which are false or unnecessary for the decoding of rotary dialed phone pulses. Said false or undesired signals, for the purpose of the proper decoding of phone pulses, may be present on the phone lines as a result of the rotary phones themselves, from which the decoder apparatus of this invention receives audiofrequency signals, or may be caused by echoes or noises inherent in telephone lines.
  • the decoder apparatus of the invention consists of a device capable of converting certain audiofrequency signals into logic data or into single pulses.
  • phone pulses In the conversation state (closed d.c. current circuit), phone pulses do not operate in the rotary dialing mode prior to the establishment of the conversation, that is, by sending d.c. current pulses, but due to the inductive- capacitive connection between both phone sets in conversation and the exchange. It is only possible to transmit audiofrequency signals produced by the operation of a rotary phone after the inductive-capacitive connection has been established.
  • Audiofrequency signals produced by a rotary phone and captured by the decoder apparatus during predetermined time spaces, allow conversion to logic data or single pulses of the number or character sent through rotary dialing.
  • the decoder apparatus receives the audiofrequency signals produced by the rotary phone with the characteristics inherent to its maintenance condition, its system, brand, etc. These audiofrequency signals normally appear within certain time periods (in this example, we refer to those phone systems which operate with a pulse rate wherein the number "0" will originate ten pulses with an approximate duration each of 100 milliseconds). Said audiofrequency signals are transformed into square wave signals in order to allow their digital processing (by means of the microprocessor in said decoder apparatus) and are then transformed into logic data or into single pulses.
  • Said audiofrequency signals (in this example originated by rotary dialing of number "3") are captured by applying the method disclosed in this invention, in the following predetermined time periods:
  • this new audiofrequency signal Upon receipt of this new audiofrequency signal, another period is initiated of approximately 50 milliseconds such as indicated in (A), after which the signal necessary for converting into logic data or into a single pulse the audiofrequency information originated by the second phone pulse produced by the rotary phone appears in the second time period of approximately 30 milliseconds.
  • This example refers to the decoding of audiofrequency signals originated by the rotary dialing of number "3". Therefore, when, after receipt of the third rotary pulse the following fourth time period elapses, initiated as from the ending of the previous third time period, no other audiofrequency signal will appear within the approximately 50 milliseconds of the fourth time period.
  • the decoder apparatus will neither capture a new audiofrequency signal nor generate new logic data or another single pulse during this time period.
  • the decoder will neither accept nor convert into logic data or into single pulses other audiofrequency signals, since the ending of the phone pulse train originated in the rotary dialing of number "3" has taken place.
  • the decoder has converted into logic data or into single pulses the audiofrequency signals produced by a three-phone pulse train (rotary dialing of number "3").
  • FIG. 1 shows a block diagram of the basic apparatus for recognizing the presence of a phone pulse train in the form of audiofrequency signals, originated through rotary dialing on a phone line after closure of the d.c. current circuit.
  • FIG. 2 is a block diagram showing how the apparatus recognizes phone pulses in the form of audiofrequency signals originated through rotary dialing on a phone line after closure of the d.c. current circuit and converts said signals into binary-type information.
  • FIGS. 3 and 4 respectively, illustrate the main circuitry as to how the block diagrams of FIGS. 1 and 2 can be carried into practice.
  • FIG. 1 Let us now describe in detail FIG. 1, bearing in mind that what is wanted is to recognize the presence of a phone pulse train when said pulses appear as audiofrequency signals after the conversation period has been established.
  • the phone line is connected to input E of block 1, which includes an input limiter or trimmer intended to prevent the overloading of the subsequent circuits in the cases of phone pulses signals with higher levels than those set by said trimmer.
  • Audiofrequency signals thus processed are applied to circuit or block 2, which includes a series of amplifiers and bandpass filters intended for recovering, within the audiofrequency spectrum present in the signals produced by phone pulse trains, the most significant and available portions of these signals.
  • the output of block 2 is coupled to the input of block 3 after the incorporation of a level regulator 2'.
  • This regulator is intended for maintaining a certain level of the audiofrequency signals before they enter circuit or block 3, and its adjustment depends on the conditions offered by the phone lines making up the communication between the phone set generating the call and the referenced decoder apparatus, as well as on the characteristics of the exchanges engaged in said communications.
  • the system thus conceived is intended for obtaining correct decoding or recognition of the signals produced by phone pulses, based on a preadjustable level of said signals.
  • the signals after their adjustment by means of regulator 2', enter input of block 3, which includes a SCHMITT-TRIGGER.
  • the rectifier portion thereof is intended for recovering only the positive portion of the audiofrequency signal cycles.
  • Signals thus rectified are introduced into the SCHMITT-TRIGGER in order to transform them into square waves, this being the only form of energy which can be introduced into digital logical elements in order to process their levels and times.
  • Square wave signals present at the output of block 3 enter the integrator 4.
  • the integrator which has, as an essential purpose, the conversion of the two consecutive square wave signals corresponding to the audiofrequency signals produced by each phone pulse into a single pulse.
  • the integrator may be embodied as a microprocessor as discussed with respect to FIG. 2. Said conversion requires microprocessor to analyze times and compare intervals. If the time period between the first and second square wave signals coming from the trigger ranges from 50 to 80 milliseconds, the microprocessor generates a single pulse.
  • microprocessor interprets the end of a pulse train and stops processing information when, after receiving a second square wave signal within the time period ranging from 50 to 80 milliseconds (approximately) as from the appearance of the first square wave signal it does not detect the presence of a new square wave signal within the time period ranging from 30 to 80 milliseconds (approximately) as from the appearance of said second square wave signal and thus, it is inhibited from processing information coming from the trigger during a time period of approximately 300 milliseconds, in order to prevent the detection of noises, erratic pulses, etc.
  • the inter train inhibit time can be extended to, e.g., 1.4 seconds.
  • the microprocessor is set in such a way that it only interprets as a true phone pulse that being determined by the capture of square wave signals within the time periods set forth in the method disclosed in the present invention. For instance, if a square wave signal supposedly originated in an audiofrequency signal produced by a rotary phone enters the microprocessor and, after a 50 (approximately) millisecond time period has elapsed and within a subsequent 30 millisecond time period, no other square wave signal is captured, the microprocessor ignores said square wave signal and does not therefore generate a single pulse.
  • Square wave signals transformed into single pulses by block 4 enter the decimal-type counter 5 having, e.g., ten outputs. In this particular case, it can be seen that one of said outputs has been connected to an availability or received pulse indicator means 6.
  • blocks 1, 2 and 3 have characteristics and functions identical to those previously described for FIG. 1.
  • signal level regulator 2' has been replaced by a follower-mode connected operational amplifier.
  • Amplifier 2' has a unitary amplification factor and, thus, performance of this decoder configuration is independent from the signal levels present in the communication between the signal generating calling phone set and the decoder.
  • programmable interval comparator 11 is composed of timers which time constants are regulated by a time or clock signal-based generator.
  • the programmable comparator is embodied as a microprocessor (in this context, the word "microprocessor” means the electronic component proper plus the peripheral circuits and at least ROM memory 12).
  • microprocessor 11 not only converts the square wave signals, but also compares them with a four digit code stored in ROM 12.
  • Output 11' of microprocessor 11 enters a four-digit display 13 .
  • microprocessor 11 controls through its output 11" the utilization circuit represented by block 14.
  • this arrangement enables display 13 to exhibit any character or number corresponding to each decoded pulse train, even though there is no coincidence between the latter and the data stored in the associated memory, therefore not activating utilization circuit 14.
  • FIG. 3 represents a practical display of the block diagram of FIG. 1; therein the phone line enters coupling transformer 3 through terminals TER 1 and TER 2.
  • Transformer T3 has an impedance equal to or approximate to that of a common phone set with its receiver unhooked.
  • One terminal of said transformer is ground-connected in order to allow its coupling to the input of operational amplifier A8; thus the return of all signals being processed by the apparatus is connected to a common point or ground.
  • Capacitor C4 and resistor R5 form the first input filter for trimming or attenuating the most significant portion of the signals in their high-frequency spectrum.
  • Zenner-type diodes D6 and D7 restrict the amplitude of the signals produced by phone pulses to a certain value with the object of protecting the first operational amplifier A8.
  • This amplifier is configured in the follower or buffer mode, thus presenting no amplification factor.
  • the configuration of these two amplifiers results in a bandpass-type filter, the response of which is determined by capacitors C10 and C13 and by resistors 11 and 14.
  • the function of this filter is that of recovering the most significant or useful portions of the signals to be analyzed, and eliminating the extraneous signals and noise components accompanying the phone pulses.
  • Filtered signals are then sent to amplifier A16 through variable resistor level regulator REG 15.
  • the audio level and gain factor of amplifier A16 depend on the conditions of the phone line to which the apparatus is connected, as well as on the attenuation factors presented by phone nets.
  • the output of the amplifier A16 is connected to the input of amplifier A17, the circuit configuration of which allows the rectified output of the signals to be analyzed, therefore eliminating one of the semi-cycles of said signals.
  • positive semi-cycles enter one of the inputs of gate G18, which is of the NAND-SCHMITT-TRIGGER type, with the object of converting the analog character of the signals into square waves, this condition being indispensable to their use in digital processing components.
  • the remaining input of gate G18 is set to a certain bias so that said gate works as a level detector or threshold detector. This configuration supplements what has been described for the operating characteristics of amplifier A16.
  • the reason for setting a level for signal detection, by gate G18 is due to the presence of the high dynamic range which phone pulses have, in the form of audiofrequency signals.
  • Each phone pulse originated by the operation of the dial of a rotary phone set on a phone line in a conversation state consists of two signals, one corresponding to the time the contact opens and the other corresponding to the time the contact closes. This means that, at the output of gate G18, we have for each signal received at the input of the apparatus, two successive square wave signals which are produced within a time period of approximately 80 milliseconds.
  • the essential parameters on which the decoding of phone pulses thus originated are based are the following:
  • the single pulse produced by the microprocessor within the approximately 80 millisecond time period is valid because the apparatus detects the presence of two successive signals, the rising fronts of which take place within an approximately 80 millisecond time period.
  • Erratic signals or the presence of a single signal in the apparatus are not considered valid, since they do not represent a real opening-closure in a rotary phone.
  • the phone pulse (or each one of the phone pulses) is divided into two audiofrequency signals.
  • the device interprets or analyzes the transition period between two successive signals, the rising fronts of which take place within an approximately 80 millisecond time period.
  • the decoder apparatus interprets when any phone pulse train has finished, as described at the SUMMARY OF THE INVENTION and in the detailed description of FIG. 1.
  • said signals For the purpose of performing the processing of the pair of square wave signals present at the output of gate G18, said signals enter integrator 19, the output of which offers a single pulse per each pair of incoming square wave signals. Said single pulse is used to command the decimal-type counter 20. The latter has an "n" output capacity.
  • a switching transistor 22 and a luminous indicator 21 are connected at output 205 of counter 20. The configuration thus constituted results in the activation of luminous indicator 21 if the audiofrequency signals corresponding to the number 5 pulse train produced by a rotary phone set enter terminals 1 and 2 of the apparatus.
  • FIG. 4 represents a practical display of the FIG. 2 block diagram.
  • FIG. 4 shows a circuit variation from the NAND-SCHMITT-TRIGGER gate G18. Output of the latter enters microprocessor 34. Said microprocessor decodes square wave signals originating from audiofrequency signals produced by phone pulse trains in the same way as described for FIG. 3 and the SUMMARY OF THE INVENTION. pulses present at the gate G18 output enter microprocessor 34 which transforms square wave signals into binary information. Said binary information shows up at outputs 23', 23", 23"' and 23"" of microprocessor 34. Said outputs are connected to decoder circuit 26 which is of the binary to seven segments exciter type. Output 26' of decoder 26 produces the excitation of each one of the display 31 seven segment indicators, whereas transistors 30', 29', 28' and 27' are programmed so as to keep the indicator in the latch state.
  • the decoded information is also compared in one of microprocessor 34 associated memories.
  • the logic data corresponding to, e.g., four decoded pulse trains are compared.
  • microprocessor 34 provides at its output 24 logic signals which produce acoustic signals through transistor 32 and piezoelectric buzzer 33. It must be remembered that numeric indicator 31 is always enabled to exhibit any decoded character or number, even though the latter does not correspond to logic data stored in one of said microprocessor 34 associated memories.
  • microprocessor 34 Upon the decoding of the four pulse trains, microprocessor 34 is inhibited from decoding additional pulse trains. This is due to the fact that the numeric indicator 31 illustrated in the present arrangement only has 4 digits.
  • An example of the possibilities that a microprocessor can offer for the decoding of phone pulses is that of varying the time constants in order to capture square wave signal rising fronts.
  • This possibility can be employed when the phone pulse speed is unusual or when mechanical or electronic generators with a rhythm different to that of conventional phone sets are employed for the transmission of dialing pulses or characters.
  • the conventional exchanges accept up to 450 milliseconds as the so called interdigital time.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Telephone Function (AREA)
US06/479,026 1982-03-31 1983-03-25 Method and apparatus for decoding audiofrequency information sent through rotary dialing Expired - Fee Related US4618742A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AR288969 1982-03-31
AR288969A AR229828A1 (es) 1982-03-31 1982-03-31 Aparato para decodificar informacion de audiofrecuencia enviada por discado desde un aparato telefonico llamante durante el periodo de conferencia establecida con un aparato telefonico o llamado

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US06/833,275 Continuation-In-Part US4771450A (en) 1982-03-31 1986-02-27 Method and apparatus for converting rotary signals to audiofrequency signals

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2214384A (en) * 1988-01-04 1989-08-31 Lam Sek Wai A control system for use with a telephone system
US5050187A (en) * 1988-04-12 1991-09-17 The Furukawa Electric Co., Ltd. Communication system equipped with an AC coupling receiver circuit
US5144652A (en) * 1989-03-13 1992-09-01 Smits Johannes H M Device for connecting a subscriber line to a selected internal line
US5638435A (en) * 1995-05-12 1997-06-10 Telefonaktiebolaget Lm Ericsson Impulse signal convertor

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4006316A (en) * 1974-08-12 1977-02-01 International Mobile Machines Corporation Code-controlled detection and function actuating system
US4121053A (en) * 1977-05-05 1978-10-17 Dick William J Telephone command apparatus
US4446339A (en) * 1982-04-26 1984-05-01 International Mobile Machines Corporation Rotary dial decoder

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4006316A (en) * 1974-08-12 1977-02-01 International Mobile Machines Corporation Code-controlled detection and function actuating system
US4121053A (en) * 1977-05-05 1978-10-17 Dick William J Telephone command apparatus
US4446339A (en) * 1982-04-26 1984-05-01 International Mobile Machines Corporation Rotary dial decoder

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2214384A (en) * 1988-01-04 1989-08-31 Lam Sek Wai A control system for use with a telephone system
US5050187A (en) * 1988-04-12 1991-09-17 The Furukawa Electric Co., Ltd. Communication system equipped with an AC coupling receiver circuit
US5144652A (en) * 1989-03-13 1992-09-01 Smits Johannes H M Device for connecting a subscriber line to a selected internal line
US5638435A (en) * 1995-05-12 1997-06-10 Telefonaktiebolaget Lm Ericsson Impulse signal convertor

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